Old Irish (Old Irish: Goídelc; Irish: Sean-Ghaeilge; Scottish Gaelic: Seann Ghàidhlig; Manx: Shenn Yernish; sometimes called Old Gaelic[2][3]) is the name given to the oldest form of the Goidelic languages for which extensive written texts are extant. It was used from c.600 to c.900. The primary contemporary texts are dated c.700–850; by 900 the language had already transitioned into early Middle Irish. Some Old Irish texts date from the 10th century, although these are presumably copies of texts composed at an earlier time period. Old Irish is thus the ancestor of Modern Irish, Manx, and Scottish Gaelic.[2]

Old Irish is known for having a particularly complex system of morphology and especially of allomorphy (more or less unpredictable variations in stems and suffixes in differing circumstances) as well as a complex sound system involving grammatically significant consonant mutations to the initial consonant of a word. Apparently,[* 1] neither characteristic was present in the preceding Primitive Irish period. Much of the complex allomorphy was subsequently lost, but the sound system has been maintained with little change in the modern languages.

Contemporary Old Irish scholarship is still greatly influenced by the works of a small number of scholars active in the late 19th and early 20th centuries such as Rudolf Thurneysen (1857–1940) and Osborn Bergin (1873–1950).

A system of conjugated prepositions that is unusual in Indo-European languages (although they are found in many Semitic languages such as Arabic): dím "from me", dít "from you", de "from him", di "from her", diib "from them" (basic preposition di "from"). There is a great deal of allomorphy here, as well.

Infixed object prepositions, which are inserted between the verb stem and its prefix(es). If a verb lacks any prefixes, a dummy prefix is normally added.

Special verbal conjugations are used to signal the beginning of a relative clause

Old Irish also preserves most aspects of the complicated Proto-Indo-European (PIE) system of morphology. Nouns and adjectives are declined in three genders (masculine, feminine, neuter); three numbers (singular, dual, plural); and five cases (nominative, vocative, accusative, dative and genitive). Most PIE noun stem classes are maintained (o-, yo-, ā-, yā-, i-, u-, r-, n-, s-, and consonant stems). Most of the complexities of PIE verbal conjugation are also maintained, and there are new complexities introduced by various sound changes (see below).

A still older form of Irish is known as Primitive Irish. Fragments of Primitive Irish, mainly personal names, are known from inscriptions on stone written in the Ogham alphabet. The inscriptions date from about the 4th to the 6th centuries. Primitive Irish appears to have been very close to Common Celtic, the ancestor of all Celtic languages, and it had a lot of the characteristics of other archaic Indo-European languages.

Relatively little survives in the way of strictly contemporary sources. They are represented mainly by shorter or longer glosses on the margins or between the lines of religious Latinmanuscripts, most of them preserved in monasteries in Germany, Italy, Switzerland, France and Austria, having been taken there by early Irish missionaries. Whereas in Ireland, many of the older manuscripts appear to have been worn out through extended and heavy use, their counterparts on the Continent were much less prone to the same risk because once they ceased to be understood, they were rarely consulted.[4]

The earliest Old Irish passages may be the transcripts found in the Cambrai Homily, which is thought to belong to the early 8th century. The Book of Armagh contains texts from the early 9th century. Important Continental collections of glosses from the 8th and 9th century include the Würzburg Glosses (mainly) on the Pauline Epistles, the Milan Glosses on a commentary to the Psalms and the St Gall Glosses on Priscian's Grammar.

In addition to contemporary witnesses, the vast majority of Old Irish texts are attested in manuscripts of a variety of later dates. Manuscripts of the later Middle Irish period, such as the Lebor na hUidre and the Book of Leinster, contain texts, which are thought to derive from written exemplars in Old Irish now lost and retain enough of their original form to merit classification as Old Irish.

The preservation of certain linguistic forms current in the Old Irish period may provide reason to assume that an Old Irish original directly or indirectly underlies the transmitted text or texts.

Some details of Old Irish phonetics are not known. /sʲ/ may have been pronounced [ɕ] or [ʃ], as in Modern Irish. /hʲ/ may have been the same sound as /h/ or /xʲ/. The precise articulation of the fortis sonorants/N/, /Nʲ/, /L/, /Lʲ/, /R/, /Rʲ/ is unknown, but they were probably longer, tenser and generally more strongly articulated than their lenis counterparts /n/, /nʲ/, /l/, /lʲ/, /r/, /rʲ/, as in the Modern Irish and Scottish dialects that still possess a four-way distinction in the coronalnasals and laterals. /Nʲ/ and /Lʲ/ may have been pronounced [ɲ] and [ʎ] respectively. The difference between /R(ʲ)/ and /r(ʲ)/ may have been that the former were trills while the latter were flaps. /m(ʲ)/ and /ṽ(ʲ)/ were derived from an original fortis–lenis pair.

Old Irish had distinctive vowel length in both monophthongs and diphthongs. Short diphthongs were monomoraic, taking up the same amount of time as short vowels, while long diphthongs were bimoraic, the same as long vowels. (This is much like the situation in Old English but different from Ancient Greek whose shorter and longer diphthongs were bimoraic and trimoraic, respectively: /ai/ vs. /aːi/.) The inventory of Old Irish long vowels changed significantly over the Old Irish period, but the short vowels changed much less.

1Both /e₁ː/ and /e₂ː/ were normally written é but must have been pronounced differently because they have different origins and distinct outcomes in later Old Irish. /e₁ː/ stems from Proto-Celtic *ē (< PIE *ei), or from ē in words borrowed from Latin. e₂ː generally stems from compensatory lengthening of short *e because of loss of the following consonant (in certain clusters) or a directly following vowel in hiatus. It is generally thought that /e₁ː/ was higher than /e₂ː/.[5] Perhaps /e₁ː/ was [eː] while /e₂ː/ was [ɛː]. They are clearly distinguished in later Old Irish, in which /e₁ː/ becomes ía (but é before a palatal consonant). /e₂ː/ becomes é in all circumstances. Furthermore, /e₂ː/ is subject to u-affection, becoming éu or íu, while /e₁ː/ is not.

2A similar distinction may have existed between /o₁ː/ and /o₂ː/, both written ó, and stemming respectively from former diphthongs (*eu, *au, *ou) and from compensatory lengthening. However, in later Old Irish both sounds appear usually as úa, sometimes as ó, and it is unclear whether /o₂ː/ existed as a separate sound any time in the Old Irish period.

3/ou/ existed only in early archaic Old Irish (c.700 or earlier); afterwards it merged into /au/. Neither sound occurred before another consonant, and both sounds became ó in later Old Irish (often ú or u before another vowel). The late ó does not develop into úa, suggesting that áu > ó postdated ó > úa.

1Early Old Irish /ai/ and /oi/ merged in later Old Irish. It is unclear what the resulting sound was, as scribes continued to use both aí and oí to indicate the merged sound. The choice of /oi/ in the table above is somewhat arbitrary.

The distribution of short vowels in unstressedsyllables is a little complicated. All short vowels may appear in absolutely final position (at the very end of a word) after both broad and slender consonants. The front vowels /e/ and /i/ are often spelled ae and ai after broad consonants, which might indicate a retracted pronunciation here, perhaps something like [ɘ] and [ɨ]. All ten possibilities are shown in the following examples:

The distribution of short vowels in unstressed syllables, other than when absolutely final, was quite restricted. It is usually thought that there were only two allowed phonemes: /ə/ (written a, ai, e or i depending on the quality of surrounding consonants) and /u/ (written u or o). The phoneme /u/ tended to occur when the following syllable contained an *ū in Proto-Celtic (for example, dligud/ˈdʲlʲiɣuð/ "law" (dat.) < PC *dligedū), or after a broad labial (for example, lebor/ˈLʲevor/ "book"; domun/ˈdoṽun/ "world"). The phoneme /ə/ occurred in other circumstances. The occurrence of the two phonemes was generally unrelated to the nature of the corresponding Proto-Celtic vowel, which could be any monophthong: long or short.

Long vowels also occur in unstressed syllables. However, they rarely reflect Proto-Celtic long vowels, which were shortened prior to the deletion (syncope) of inner syllables. Rather, they originate in one of the following ways:

from the late resolution of a hiatus of two adjacent vowels (usually as a result of loss of *s between vowels);

Stress is generally on the first syllable of a word. However, in verbs it occurs on the second syllable when the first syllable is a clitic (the verbal prefix as- in as·beir/asˈberʲ/ "he says"). In such cases, the unstressed prefix is indicated in grammatical works with a following centre dot (·).

As with most medieval languages, the orthography of Old Irish is not fixed, so the following statements are to be taken as generalisations only. Individual manuscripts may vary greatly from these guidelines.

The following table indicates the broad pronunciation of various consonant letters in various environments:

Consonant letter

Word-initial

After a vowel

unmutated

nasalised

lenited

b

/b/

—

/v/

c

/k/

/ɡ/

—

/k, ɡ/

d

/d/

—

/ð/

f

/f/

/v/

silent

/f/

g

/ɡ/

—

/ɣ/

h

See discussion below

l

/L/

/l/

m

/m/

/ṽ/

n

/N/

/n/

p

/p/

/b/

—

/p, b/

r

/R/

/r/

s

/s/

/h/

/s/

t

/t/

/d/

—

/t, d/

Notes:

A dash (—) in an entry indicates that the respective consonant sound is spelled differently under the respective mutation (lenition or nasalisation) and so the indicated consonant letter does not occur then (the spelling c does not occur in a leniting environment; instead, ch /x/ does). See the next two entries.

When initial s stemmed from Primitive Irish *sw-, its lenited version is f (written and pronounced).

The slender (palatalised) variants of the above consonants occur in the following environments:

before a written e, é, i, í;

after a written i, when not followed by a vowel letter (but not after the diphthongs aí, oí, uí).

Although Old Irish has both a sound /h/ and a letter h, there is no consistent relationship between the two. Vowel-initial words are sometimes written with an unpronounced h, especially if they are very short (the prepositioni "in" was sometimes written hi) or if they need to be emphasised (the name of Ireland, Ériu, was sometimes written Hériu). On the other hand, words that begin with the sound /h/ are usually written without it: a ór/a hoːr/ "her gold". If the sound and the spelling co-occur, it is by coincidence, as ní hed/Nʲiː heð/ "it is not".

After a vowel or l, n, or r the letters c, p, t can stand for either voiced or voiceless stops; they can also be written double with either value:

Old Irish

Pronunciation

English

mac or macc

/mak(k)/

son

bec or becc

/bʲeɡ(ɡ)/

small

op or opp

/ob(b)/

refuse

brat or bratt

/brat(t)/

mantle

brot or brott

/brod(d)/

goad

derc

/dʲerk/

hole

derc

/dʲerɡ/

red

daltae

/daLte/

fosterling

celtae

/kʲeLde/

who hide

anta

/aNta/

of remaining

antae

/aNde/

who remain

Geminate consonants appear to have existed at the beginning of the Old Irish period but were simplified by the end, as is generally reflected by the spelling generally although double ll, mm, nn, rr were eventually repurposed to indicate nonlenited variants of those sounds in certain positions.

After a vowel the letters b, d, g stand for the fricatives /v, ð, ɣ/ or their slender equivalents:

Old Irish

Pronunciation

English

dub

/duv/

black

mod

/moð/

work

mug

/muɣ/

slave

claideb

/klaðʲəv/

sword

claidib

/klaðʲəvʲ/

swords

After m, b is a stop, but after d, l and r, it is a fricative:

Old Irish

Pronunciation

English

imb

/imʲbʲ/

butter

odb

/oðv/

knot (in a tree)

delb

/dʲelv/

image

marb

/marv/

dead

After n and r, d is a stop:

Old Irish

Pronunciation

English

bind

/bʲiNʲdʲ/

melodious

cerd

/kʲeRd/

"art, skill"

After n, l, and r, g is usually a stop, but it is a fricative in a few words:

After vowels m is usually a fricative, but sometimes a (nasal) stop, in which case it is also often written double:

Old Irish

Pronunciation

English

dám

/daːṽ/

company

lom or lomm

/Lom/

bare

The digraphs ch, ph, th do not occur in word-initial position except under lenition, but wherever they occur, they are pronounced /x/, /f/, /θ/.

Old Irish

Pronunciation

English

ech

/ex/

horse

oíph

/oif/

beauty

áth

/aːθ/

ford

The letters l, n, and r are generally written double when they indicate the tense sonorants, single when they indicate the lax sonorants. Originally, it reflected an actual difference between single and geminate consonants, as tense sonorants in many positions (such as between vowels or word-finally) developed from geminates. As the gemination was lost, the use of written double consonants was repurposed to indicate tense sonorants. Doubly written consonants of this sort do not occur in positions where tense sonorants developed from non-geminated Proto-Celtic sonorants (such as word-initially or before a consonant).

Written vowels a, ai, e, i in poststressed syllables (except absolutely word-finally) all seem to represent phonemic /ə/. The particular vowel that appears is determined by the quality (broad vs. slender) of the surrounding consonants and has no relation to the etymological vowel quality:

Old Irish was affected by a series of phonological changes that radically altered its appearance compared with Proto-Celtic and older Celtic languages (such as Gaulish, which still had the appearance of typical early Indo-European languages such as Latin or Ancient Greek). The changes were such that Irish was not recognized as Indo-European at all for much of the 19th century. The changes must have happened quite rapidly, perhaps in only one or two hundred years around 500–600, because almost none of the changes are visible in Primitive Irish (4th to 6th centuries), and all of them are already complete in archaic Old Irish (8th century). A capsule summary of the most important changes is (in approximate order):[8][9]

Syllable-final *n (from PIE *m, *n) assimilated to the following phoneme, even across word boundaries in the case of syntactically connected words.

Voiceless stops became voiced: *mp *nt *nk > /b d ɡ/.

Voiced stops became prenasalised /ᵐb, ⁿd, ᵑɡ/. They were reduced to simple nasals during the Old Irish period.

Before a vowel, /n-/ was attached to the beginning of the syllable.

Lenition of all single consonants between vowels. That applied across word boundaries in the case of syntactically connected words.

Stops became fricatives.

*s became /h/ (later lost unless the following syllable was stressed).

Extensive umlaut ("affection") of short vowels, which were raised or lowered to agree with the height of following Proto-Celtic vowels. Similarly, rounding of *a to /o/ or /u/ often occurred adjacent to labial consonants.

Both the palatalised ("slender") and lenited variants of consonants were phonemicised, multiplying the consonant inventory by four (broad, broad lenited, slender, slender lenited). Variations between broad and slender became an important part of the grammar:

Lenition and nasal assimilation across word boundaries in syntactically connected words produced extensive sandhi effects (Irish initial mutations). The variations became an important part of the grammar.

Both umlaut (vowel affection) and especially syncope radically increased the amount of allomorphy found across declensions and conjugations. The most dramatic deviations are due to syncope: compare as·berat "they say" vs. ní-epret "they do not say" or do·rósc(a)i "he surpasses" vs. ní-derscaigi "he does not surpass" (where the stressed syllable is boldfaced).

These various changes, especially syncope, produced quite complex allomorphy, because the addition of prefixes or various pre-verbal particles (proclitics) in Proto-Celtic changed the syllable containing the stress: According to the Celtic variant of Wackernagel's law, the stress fell on the second syllable of the verbal complex, including any prefixes and clitics. By the Old Irish period, most of this allomorphy still remained, although it was rapidly eliminated beginning in the Middle Irish period.

Among the most striking changes are in prefixed verbs with or without pre-verbal particles. With a single prefix and without a proclitic, stress falls on the verbal root, which assumes the deuterotonic ("second-stressed") form. With a prefix and also with a proclitic, stress falls on the prefix, and the verb assumes the prototonic ("first-stressed") form. Rather extreme allomorphic differences can result:

Example differences between deuterotonic and prototonic forms of various verbs. Stress falls directly after the center dot or hyphen.[17]

Earlier form

Deuterotonic

Meaning

Prototonic

Meaning

*ess-bero(n)t < PIE *-bʰeronti

as·berat/as-ˈbʲerəd/

they say

ní-epret /Nʲiː-ˈhebrʲəd/

they do not say

*cum-uss-ana

con·osna

he rests

ní-cumsana

he does not rest

*de-ro-uss-scochi

do·rósc(a)i

he surpasses

ní-derscaigi

he does not surpass

*de-lugi < PIE *-logʰeyeti

do·lug(a)i

he pardons

ní-dílg(a)i

he does not pardon

*de-ro-gn...

do·róna

he may do

ní-derna

he may not do

The following table shows how these forms might have been derived:

Possible derivation of some verbal forms

"they say"

"they do not say"

"he rests"

"he does not rest"

"he surpasses"

"he does not surpass"

Post-PIE

eks bʰeronti

nē eks bʰeronti

kom uks h₂eneh₂ti

nē kom uks h₂eneh₂ti

dē pro uks skokeyeti

nē dē pro uks skokeyeti

Proto-Celtic

eks ˈberonti

nī ˈeks-beronti

kom ˈuks-anāti

nī ˈkom-uks-anāti

dī ˈɸro-uks-skokīti

nī ˈdī-ɸro-uks-skokīti

Early Irish

ess-es ˈberont

ní-s ˈess-beront

kon-es ˈuss-anát

ní-s ˈkom-uss-anát

dí-s ˈro-uss-skokít

ní-s ˈdi-ro-uss-skokít

Nasal assimilation

ess-es ˈberodd

ní-s ˈess-berodd

—

—

—

—

Lenition

es-eh ˈberod

Ní-h ˈes-berod

kon-eh ˈus-anáθ

Ní-h ˈkow̃-us-anáθ

dí-h ˈRo-us-skoxíθ

Ní-h ˈdi-ro-us-skoxíθ

Palatalization

es-eh ˈbʲerod

Nʲí-h ˈes-bʲerod

—

Nʲí-h ˈkow̃-us-anáθ

dʲí-h ˈRo-us-skoxʲíθ

Nʲí-h ˈdʲi-ro-us-skoxʲíθ

Hiatus reduction

—

—

—

—

dʲí-h ˈRós-skoxʲíθ

Nʲí-h ˈdʲi-rós-skoxʲíθ

Umlaut (vowel affection)

—

—

kon-eh ˈos-anáθ

Nʲí-h ˈkuw̃-us-anáθ

—

Nʲí-h ˈdʲe-rós-skoxʲíθ

Shortening of absolutely final vowel

—

—

—

—

—

—

Loss/assimilation of final consonant(s)

es-e bʲ-ˈbʲerod

Nʲí h-ˈes-bʲerod

kon-e h-ˈos-aná

Nʲí k-ˈkuw̃-us-aná

dʲí R-ˈRós-skoxʲí

Nʲí d-ˈdʲe-rós-skoxʲí

Mora reduction in unstressed final vowel

es bʲ-ˈbʲerod

—

kon h-ˈos-ana

Nʲí k-ˈkuw̃-us-ana

dʲí R-ˈRós-skoxʲi

Nʲí d-ˈdʲe-rós-skoxʲi

Consonant assimilation

es ˈbʲerod

Nʲí h-ˈebʲ-bʲerod

kon h-ˈos-ana

Nʲí k-ˈkuw̃-us-ana

dʲí R-ˈRós-skoxʲi

Nʲí d-ˈdʲe-rós-skoxʲi

Syncope

es ˈbʲerod

Nʲí h-ˈebʲbʲrod

kon h-ˈosna

Nʲí k-ˈkuw̃sana

dʲí R-ˈRósskxʲi

Nʲíd-ˈdʲersskoxʲi

Further consonant assimilation

—

Nʲí h-ˈebʲbʲrʲod

kon ˈosna

—

dʲí R-ˈRósski

Nʲíd-ˈdʲerskoxʲi

Unstressed vowel reduction

es ˈbʲerəd

Nʲí h-ˈebʲbʲrʲəd

—

Nʲí k-ˈkuw̃səna

di R-ˈRósski

Nʲí d-ˈdʲerskəxʲi

Prepositional modification

as ˈbʲerəd

—

—

—

do R-ˈRósski

—

Geminate reduction (non-vocalic-adjacent); sandhi geminate reduction

as·ˈbʲerəd

Nʲíh-ˈebrʲəd

kon·ˈosna

Nʲí-ˈkuw̃səna

do·ˈRóski

Nʲí-ˈdʲerskəxʲi

Fricative voicing between unstressed syllables

—

—

—

—

—

Nʲíd-ˈdʲerskəɣʲi

Old Irish pronunciation

as·ˈbʲerəd

Nʲí-h-ˈebrʲəd

kon·ˈosna

Nʲí-ˈkuw̃səna

do·ˈRóski

Nʲí-ˈdʲerskəɣʲi

Old Irish spelling

as·berat

ní-epret

con·osna

ní-(c)cumsana

do·rósc(a)i

ní-(d)derscaigi

The most extreme allomorphy of all came from the third person singular of the s-subjunctive because an athematic person marker -t was used, added directly onto the verbal stem (formed by adding -s directly onto the root). That led to a complex word-final cluster, which was deleted entirely. In the prototonic form (after two proclitics), the root was unstressed and thus the root vowel was also deleted, leaving only the first consonant:

In more detail, syncope of final and intervocalic syllables involved the following steps (in approximate order):

Shortening of absolutely final long vowels.

Loss of most final consonants, including *m, *n, *d, *t, *k, and all clusters involving *s (except *rs, *ls, where only the *s is lost).

Loss of absolutely final short vowels (including those that became final as a result of loss of a final consonant and original long final vowels).

Shortening of long vowels in unstressed syllables.

Collapsing of vowels in hiatus (producing new unstressed long vowels).

Syncope (deletion) of vowels in every other interior unstressed syllable following the stress. If there are two remaining syllables after the stress, the first one loses its vowel; if there are four remaining syllables after the stress, the first and third lose their vowel.

Resolution of impossible clusters resulting from syncope and final-vowel deletion:

*l *r *n not adjacent to a vowel became syllabic and then had a vowel inserted before them (e.g. domun "world" < *domn < *domnos < *dumnos; immormus "sin" < *imm-ro-mess). However, in the case of *n, that occurred only when the nasal had not previously been joined to a following voiced stop as a result of nasal assimilation: compare frecnd(a)irc "present" (disyllabic).

Remaining impossible clusters were generally simplified by deletion of consonants not adjacent to vowels (such as between other consonants). However, Old Irish tolerated geminates adjacent to other consonants as well other quite complex clusters: ainm/aNʲm/ "name" (one syllable), fedb/fʲeðβ/ "widow", do-aidbdetar/do-ˈaðʲβʲðʲədər/ "they are shown".[19]

All five Proto-Celtic short vowels (*a, *e, *i, *o, *u) survived into Primitive Irish more or less unchanged in stressed syllables.

However, during the runup to Old Irish, several mutations (umlauts) take place. Former vowels are modified in various ways depending on the following vowels (or sometimes surrounding consonants). The mutations are known in Celtic literature as affections or infections such as these, the most important ones:[20]

i-affection: Short *e and *o are raised to i and u when the following syllable contains a high vowel (*i, *ī, *u, *ū). It does not happen when the vowels are separated by certain consonant groups.

a-affection: Short *i and *u are lowered to e and o when the following syllable contains a non-high back vowel (*a, *ā, *o, *ō[clarification needed]).

u-affection: Short *a, *e, *i are broken to short diphthongs au, eu, iu when the following syllable contains a *u or *ū that was later lost. It is assumed that at the point the change operated, u-vowels that were later lost were short *u while those that remain were long *ū. The change operates after i-affection so original *e may end up as iu.

i-affection (unstressed *-es- > *-is- in Primitive Irish, also found in s-stems)

Absolute 3sg

berith

/bʲirʲəθʲ/

"he carries"

*beretis

*bʰereti + -s

Unstressed i = /ə/ with surrounding palatalised consonants; see #Orthography

Conjunct 1sg

·biur

/bʲĭŭr/

"I carry"

*beru < *berū

*bʰerō

i-affection + u-affection

Conjunct 2sg

bir

/bʲirʲ/

"you (sg.) carry"

*beris < *berisi

*bʰeresi

i-affection (unstressed *-es- > *-is- in Primitive Irish)

Conjunct 3sg

beir

/bʲerʲ/

"he carries"

*beret < *bereti

*bʰereti

i in ei signals palatalisation of following consonant; see #Orthography

The result of i-affection and a-affection is that it is often impossible to distinguish whether the root vowel was originally *e or *i (sen < *senos and fer < *wiros have identical declensions). However, note the cases of nert vs. fiurt above for which i-affection, but not a-affection, was blocked by an intervening rt.

Most instances of é and ó in nonarchaic Old Irish are due to compensatory lengthening of short vowels before lost consonants or to the merging of two short vowels in hiatus: cét/kʲeːd/ ‘hundred’ < Proto-Celtic kantom (cf. Welshcant) < PIE *kṃtóm.

Proto-Celtic *s is lenited to /h/, which then disappears between vowels. In general, Old Irish s when not word-initial stems from earlier geminate ss (often still written as such, especially in archaic sources).

Proto-Celtic *kʷ *gʷ remain in Ogam Irish (maqqi "son" (gen. sg.)) but become simple c g in Old Irish. Occasionally, they leave their mark by rounding the following vowel.

Proto-Celtic *y becomes *iy after a consonant, much as in Latin. The vowel *i often survives before a lost final vowel, partly indicating the nature of the final vowel as a result of vowel affection: cride cridi cridiu "heart" (nom. gen. dat.) < *kridion *kridiī *kridiū < *kridiyom *kridiyī *kridiyū < PIE *ḱr̥d- (e.g. gen. *ḱr̥d-és). After this, *y is lost everywhere (after palatalising a preceding consonant).

Many intervocalic clusters are reduced, becoming either a geminate consonant or a simple consonant with compensatory lengthening of the previous vowel. During the Old Irish period, geminates are reduced to simple consonants, occurring earliest when adjacent to a consonant. By the end of the Old Irish period, written ll mm nn rr are repurposed to indicate the non-lenited sounds /L m N R/ when occurring after a vowel and not before a consonant.

^ abKoch, John Thomas (2006). Celtic culture: a historical encyclopedia. ABC-CLIO. p. 831. The Old Irish of the period c. 600–c. 900 AD is as yet virtually devoid of dialect differences, and may be treated as the common ancestor of the Irish, Scottish Gaelic, and Manx of the Middle Ages and modern period; Old Irish is thus sometimes called 'Old Gaelic' to avoid confusion.

^Ó Baoill, Colm (1997). "13: The Scots-Gaelic Interface". The Edinburgh History of the Scots Language. Edinburgh University Press. p. 551. The oldest form of the standard that we have is the language of the period c. AD 600–900, usually called 'Old Irish' – but this use of the word 'Irish' is a misapplication (popular among English-speakers in both Ireland and Scotland), for that period of the language would be more accurately called 'Old Gaelic'.